​

let scores = {

  1: 100000,

  2: -100000,

};

​

​

function bestMove() {

​

  // AI to make its turn

  let bestScore = -Infinity;

  let move;

  let tempI;

​

​

​

​

​

  for (let j = 0; j < w; j++) {

    // Is the spot available?

​

    tempI = nextSpace(j);

​

​

    if (tempI >= 0) {

​

      board[tempI][j] = 1;

​

      let score = minimax(board, depth, false, 1);

​

      board[tempI][j] = 0;

​

      if (score > bestScore) {

        bestScore = score;

        move = j;

​

      }

    }

  }

​

  player = 2;

  return (move);

}

​

function score_position(player, player2, nr_moves) {

  //heuristic could be more in depth, using 

  let score = 0

​

  for (i = 1; i < h; i++) {

    for (j = 1; j < w; j++) {

      if ((countPieces(i, j, i + 4, j, player) == 3 && countPieces(i, j, i + 4, j, 0) == 1) || (countPieces(i, j, i, j + 4, player) == 3 && countPieces(i, j, i, j + 4, 0) == 1) ||

        (countDiagonal(i, j, 0, player) == 3 && countDiagonal(i, j, 1, 0) == 1)) {

        score += 1000;

      }

​

      if ((countPieces(i, j, i + 4, j, player) == 2 && countPieces(i, j, i + 4, j, 0) == 2) || (countPieces(i, j, i, j + 4, player) == 2 && countPieces(i, j, i, j + 4, 0) == 2) ||

        (countDiagonal(i, j, 0, player) == 2 && countDiagonal(i, j, 1, 0) == 2)) {

        score += 10;

      }

​

      if ((countPieces(i, j, i + 4, j, player) == 1 && countPieces(i, j, i + 4, j, 0) == 3) || (countPieces(i, j, i, j + 4, player) == 1 && countPieces(i, j, i, j + 4, 0) == 3) ||

        (countDiagonal(i, j, 0, player) == 1 && countDiagonal(i, j, 1, 0) == 3)) {

        score += 1;

​

      }

​

      if ((countPieces(i, j, i + 4, j, player2) == 3 && countPieces(i, j, i + 4, j, 0) == 1) || (countPieces(i, j, i, j + 4, player2) == 3 && countPieces(i, j, i, j + 4, 0) == 1) ||

        (countDiagonal(i, j, 0, player2) == 3 && countDiagonal(i, j, 1, 0) == 1)) {

        score -= 1000;

​

      }

​

      if ((countPieces(i, j, i + 4, j, player2) == 2 && countPieces(i, j, i + 4, j, 0) == 2) || (countPieces(i, j, i, j + 4, player2) == 2 && countPieces(i, j, i, j + 4, 0) == 2) ||

        (countDiagonal(i, j, 0, player2) == 2 && countDiagonal(i, j, 1, 0) == 2)) {

        score -= 10;

      }

​

      if ((countPieces(i, j, i + 4, j, player2) == 1 && countPieces(i, j, i + 4, j, 0) == 3) || (countPieces(i, j, i, j + 4, player2) == 1 && countPieces(i, j, i, j + 4, 0) == 3) ||

        (countDiagonal(i, j, 0, player2) == 1 && countDiagonal(i, j, 1, 0) == 3)) {

        score -= 1;

​

      }

    }

  }

​

  return score

}

​

function countPieces(i, j, i2, j2, player) {

  let pieces = 0;

​

  for (i; i < i2; i++) {

    for (j; j < j2; j++) {

      if (board[i][j] == player) {

        pieces += 1;

      }

​

    }

​

  }

  return pieces;

}

​

function countDiagonal(i, j, direction, player) {

​

  let pieces = 0;

​

  for (x = 0; x < 4; x++) {

    if (direction == 1) {

      if (i + x < h && j + x < w) {

​

        if (board[i + x][j + x] == player) {

          pieces += 1;

        }

      }

​

    } else {

      if (i + x < h && j - x < w && j - x > 0) {

​

        if (board[i + x][j - x] == player) {

          pieces += 1;

        }

​

      }

​

    }

​

  }

  return pieces;

}

​

function minimax(board, depth, isMaximizing, nr_moves) {

​

  let result = getWinner();

  if (result > 0) {

    return scores[result] - 20 * nr_moves;

  }

​

  if (result == -1) {

    return 0 - 50 * nr_moves;

  }

​

  if (depth == 0) {

    return score_position(1, 2, nr_moves);

  }

​

​

​

​

​

  if (isMaximizing) {

​

    let bestScore = -Infinity;

    for (let j = 0; j < w; j++) {

      let tempI = nextSpace(j);

​

      if (tempI < h && tempI > -1) {

​

        board[tempI][j] = 1;

​

        let score = minimax(board, depth - 1, false, nr_moves + 1);

​

        board[tempI][j] = 0;

​

        bestScore = max(score, bestScore);

      }

    }

​

    return bestScore;

​

  } else {

​

    let bestScore = Infinity;

    for (let j = 0; j < w; j++) {

      // Is the spot available?

      let tempI = nextSpace(j);

​

      if (tempI < h && tempI > -1) {

​

        board[tempI][j] = 2;

​

        let score = minimax(board, depth - 1, true, nr_moves + 1);

​

        board[tempI][j] = 0;

​

        bestScore = min(score, bestScore);

      }

    }

​

    return bestScore;

  }

}